Variable color electroluminescent lamp



Dec. 22, 1959 E. e. FRIDRICH VARIABLE COLOR ELECTROLUMINESCENT LAMPFiled Aug. 1, 195a INVENTORv ELMEE G. FE/DE/CH United States Patent ce2,918,594 VARIABLE COLOR ELECTROLUMINESCENT AMP Elmer G. Fridrich,Cleveland Heights, Ohio, assignor to General Electric Company, acorporation of New York Application August 1, 1958, Serial No. 752,532 6Claims. (Cl. 313-108) This invention relates to electroluminescent cellsor lamps, that is to lamps in which an electroluminescent phosphor isexcited by an electric field to emit light, and is particularlyconcerned with a variable color electroluminescent lamp.

An electroluminescent cell generally comprises a layer of phosphorcapable of generating light under the action of an electric field,sandwiched between a'pair of conducting plates, films or grids one ofwhich is transparent or at least light-transmitting. The color ofthelight produced is generally determined by the choice ofphosphor. Somerather minor changes in color may'be effected by varying the appliedvoltage or its frequencybut the variations in color thus obtained aregenerally not great enough to permit the lamp to be described as'avariable color lamp.

It has been proposed to make a variable color electroluminescent lamp inthe form of a sandwich containing several layers of phosphors ofdifferent colors with transparent conductive layers interleaved betweenthem. In theory at least, by selecting one or the other of the phosphorlayers to be energized, it is possible to change the color of lightproduced by the lamp. The difiiculty with this proposal is that theelectroluminescent phosphors currently available are not in generaltransparent so that the front layer or layers of phosphor will absorb avery high proportion of the light produced by the rear layer.

The object of the invention is to provide a new and improved variablecolor electroluminescent lamp.

A more specific object of the invention is to provide a variable colorelectroluminescent lamp wherein the phosphors producing the variouscolors are located in the same plane of the lamp relative to the viewerand wherein transmission of light of one color through the phosphor usedto produce light of another color is avoided.

A variable color electroluminescent lamp in accordance with theinvention comprises a composite structure of wires or conductors coatedwith phosphors alternating in color according to a cyclic pattern. Thecoated conductors are assembled in a repeating order permitting them tobe turned on one color at a time or in combination for blending ofcolors.

In a preferred embodiment, the assembly or grid of phosphor coated wiresis coated with a thin film of slightly conducting transparent lacquerover which is applied a sheat of conducting glass paper. This assemblyis then encapsulated between sheets of light transmitting thermoplasticmaterial such as polyethylene. A feature of this construction is theoptical effect of apparently more uniform brightness of the lighted areaover that of an equivalent ray of fiat strips. This effect resultsfromtherefiection and refraction of light in the valleys betweenadjacent coated wires.

For further objects and advantages and for a detailed description of apreferred variable color electroluminescent lamp in accordance with theinvention and of the manner of making same, attention is now directed tothe following description and accompanying drawing. The features of theinvention believed to be novel will be more particularly pointed out inthe appended claims.

2,918,594 Patented Dec. 22, 1959 In the drawing:

Fig. 1 is a pictorial view of a laminated variable colorelectroluminescent lamp embodying the invention, the various constituentlayers being delaminated or peeled back atone corner to show theinternal construction.

Fig. 2 is a cross sectional view to a much enlarged scale of a portionof the lamp of Fig. 1.

Fig. 3 is a pictorial view illustrating a stage in the.

making of the coated wire assembly used in the lamp of Fig. 1.

Referring to the drawing and more particularly to Figs. 1 and 2, thereis shown a flat rectangular electroluminescent lamp 1 embodying theinvention. The electrically active layers of the lamp are encapsulatedor encased between a lower sheet 2 and an upper sheet 3 of thermoplasticmaterial welded together along their margins. Examples of suitablematerials are polyethylene, polytetrafluoroethylene,chlorotrifluoropolyethylene, and polystyrene. A preferred materialconsists of high density polyethylene film of 0.003 inch thickness.

The electrical-1y active elements of the lamp comprise a layer 4 of finewires coated with phosphor and laid side by side in the form of mat. Ina three-color lamp, the wires are associated in groups of three, theWires numbered 5, 6 and 7 corresponding respectively to the colors red,green and blue indicated by conventional color hatching. Each coatedwire comprises a metal core 8, for instance of copper, an insulatingcoating 9 therearound, and a phosphor coating 10 around the insulatingcoating. The wire core 8 may consist of one mil copper wire. Theinsulating coating-9 may consist of barium titanate dispersed in asuitable high dielectric constant binder, for examplecyanoethylcellulose plasticized with cyanoethylphthalate, or an epoxyresin. Phosphor layer 10 consists of a suitable electroluminescentphosphor likewise dispersed in a high dielectric constant binder whichconveniently may be the same as that used for the insulating layer 9.The insulating layer and the phosphor layer may each be between 1 and 2mils thick so that the overall diameter of the coated wires convenientlymay be between 5 and 9 mils. The wire layer or mat may comprise forinstance 150 wires per inch in width. 7

The choice of phosphor to be included in the coatings on the wiresdepends upon the colors desired in the finished lamp. In a three-colorelectroluminiscent lamp, a suitable phosphor for the red producing wires5 is zinc sulfide activated with manganese and copper, for instanceabout 0.7% manganese and 0.15% copper. A suitable phosphor for the blueproducing wires 6 is zinc sulfide activated with copper and chlorine ina relatively low concentration, for instance 0.5 mole percent copper and0.5 mole percent chlorine prior to firing. A suitable phosphor for thegreen producing wires 7 is zinc sulfide activated with copper andchlorine with a relatively high proportion of chlorine, for instance 0.5mole percent copper and 2 mole percent chlorine in the prefiredmaterial. The foregoing phosphors have been given by way of example onlyand other phosphors known to the art and suitable for producing thecolors desired-may be used.

As best seen in Fig. 2 the assembly of phosphor coated conductors ispressed and partly embedded in a base sheet 12 of heat sensitiveflexible plastic film, adhesively treated if desired. A suitablematerial for base sheet 12 is a low density polyethylene film. A thinfilm 13 of a transparent lacquer which is at least slightly conductiveis sprayed over the coated wires to assure that the electrical fieldwill be substantially uniform over the upper half of each phors on thefront or viewing side of the cell; At the coated wire surface. Thelacquer film penetrates cusplike at least in part into the spacesbetween the coated conductors as indicated at 14; this is beneficial inachieving the desired uniformity of electric field across the phossametime it has the optical effect of increasing the apparent uniformity ofthe lighted area, that is it tends to obliterate the line structure. Asuitable material for the slightly conductive lacquer is a cement orresin such as an epoxy resin having dispersed in it a mass of conductingglass fibers. For instance a piece of conductive glass cloth may beshredded by chopping on the bias and the mass of fibers then stirredinto the cement which is then applied to provide the layer 13.

The conductive lacquer surface is considerably flatter than the corduroytextured phosphor coated wire surface proper and a sheet 15 ofconductive glass paper is applied over it. This sheet may consist ofcommercially available micro-fiber glass paper 0.001 inch thick madeconducting by dipping in a solution of indium basic trifluoroacetate andstannic chloride and then drying and baking at an elevated temperature.Alternatively a wire mesh may be used to apply voltage to the conductivelacquer instead of the conductive glass paper; the mesh should be openenough to avoid excessive obstruction of light. A thin sheet 16 of lowdensity polyethylene is placed over the conducting glass paper andserves to bind the glass paper sheet together and to the conductivelacquer layer 13 when the cell assembly is heat laminated together asshown in Fig. 1. A flattened flexible copper braid or ribbon 17 is laidbetween the glass paper sheet 15 and low density polyethylene sheet 16and has attached to it a copper screen tab 18 projecting beyond the edgeof the plastic envelope to serve as a common terminal for the lamp.Similar copper ribbons 19, 20 and 21 are connected in a repeatingpattern to every third phosphor coated wire in a manner to be moreparticularly described hereafter and corresponding to the connectionsschematically indicated in Fig. 2. These may also be provided withscreen tab terminals (not shown) similar to tab 18. Ribbon 19 connectedto phosphor coated wiresS is energized along with common terminal 18 tolight the lamp red; similarly ribbon 20 connected to wires 6 lights thelamp green and ribbon 21 connected to wires 7 lights the lamp blue. Ofcourse more than one color phosphor may be energized to produce colorblends.

To fabricate the phosphor coated wire assembly ofthe lamp, coated wireof one color, for instance blue phosphor coated wire 7, is'first woundtriple pitch on a cylinder 22 of appropriate size which has beenpre-Wrapped with heat sensitive flexible plastic'sheet 12, asillustrated in Fig. 3 wherein the wire size is much exaggerated.Flexible copper braid or ribbon 21 is placed along the length of thecylinder over spots laid bare on each turn of wire and is then coveredwithan insulating strip 23. Green phosphor coated wire 6 is then woundtriple-pitch on the cylinder in the samefashion and copper ribbon 20placed over the spots laid bare on-each turn of wire and then coveredover by insulating strip 24. Finally red phosphor coated wire is woundon the cylinder and fills the gaps between the wires already laid inplace. Copper ribbon 19 is placed over the spots laid bare and in thisway all the turns of one color are electrically joined in parallel bythe copper ribbons 19, 20 and 21. The thin film of slightly conductingtransparent lacquer may then be sprayed over the cylinder which is thenheat treated to secure the windings on backing sheet 12. The assembly isthen slit along its length, removed from the cylinder and developed intoa plane.

In laminating the various components of the electroluminiscent lamptogether, the vacuum plate technique with hydrostatic pressure appliedto the electroluminiscent lay-up over a conformable diaphragm describedin copending application Serial No. 701,906, filed December 10, 1957, ofElmer G. Fridrich and Paul A. Dell, entitled Electroluminiscent Lamp andManufacture Thereof," and assigned to the same assignee as the presentinvention, may be used.

The specific example of an embodiment of the in'ven tion given herein isintended as illustrative and not as limitative of the invention whosescope is to be determined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedState's is:

1. A variable color electroluminescent lamp comprising an assembly ofconductors laid alongside one another, said conductors being alternatelycoated with difierent color producing electroluminescent phosphors,andmeans including terminals for applying voltage to the conductorscorresponding to said different colors in order to energize selectivelysaid different color producing the phosphors.

2. A variable color electroluminescent lamp comprising an assembly ofconductors laid alongside one another, said conductors being alternatelycoated with different color producing electroluminescent phosphors,terminals for selectively energizing conductors coated with one color ofphosphor to produce a given color of light, and a transparent conductivecoating applied over said coated conductors.

3. A variable color electroluminescent lamp comprising an assembly ofconductors laid alongside one another in a plane, said conductors beingalternately coated with different color producing electroluminescentphosphors, terminals connecting the conductors of one color coating inparallel for selectively energizing the lamp to produce a given color oflight, and a transparent conductive coating applied over said coatedconductors and having a conductive terminals connected thereto to servein common for all colors.

4. A variable color electroluminescent lamp comprising a plurality offine conductors laid alongside one another in a plane, said conductorsbeing alternately coated with different color producingelectroluminetcent phosphors; conductive terminals connecting theconductors of one color coating in parallel for selectively energizingthe lamp to produce a given color of light, a coating-of a transparentlacquer which is at least slightly conducting applied on one side ofsaid coated conductors, and a sheet thereover of conductive glass fibershaving a conductive terminal connected thereto to serve in common forall colors.

5. A variable color electroluminescent lamp comprising a plurality offine wires coated with a high dielectric constant insulating materiallaid alongside one another in a plane, said wires being alternatelyovercoated with different color producing electroluminescent phosphors,conductive terminals connecting the wires of one color coating inparallel for selectively energizing the lamp to produce a given color oflight, a coating of a transparent lacquer which is at least slightlyconducting applied on one side of said coated wires, and means forapplying a voltage to said lacquer coating.

6. A laminated variable color electroluminescent lamp assemblycomprising an outer envelope of thermoplastic sheets enclosing anelectrically active assembly including a plurality of wires coated witha high dielectric constant insulating material laid alongside oneanother in a plane, said wires being alternately overcoated withdifferent color producing electroluminescent phosphors, conductiveterminals connecting the wires of one color coating in parallel forselectively energizing the lamp to produce a given color of light, acoating of a transparent lacquer which is at least slightly conductingapplied on one side of said coated wires, and a sheet thereover ofconductive glass fibers having a conductive terminal connected'theretoto serve in common for all colors.

References Cited in the file of this patent UNITED STATES PATENTS2,684,450 Mager et a1 July 20, 1954 2,730,644 Michlin Jan. 10, 19562,773,216 Edmonds Dec. 4,1956 2,792,447 Kazan May 14,1957

